Rare earth magnet is based on intermetallic compound R2T14B, thereinto, R is rare earth element, T is iron or transition metal element replacing iron or part of iron, B is boron; Rare earth magnet is called the king of the magnet as its excellent magnetic properties, the max magnetic energy product (BH)max is ten times higher than that of the ferrite magnet (Ferrite); besides, the maximum operation temperature of the rare earth magnet may reach 200° C., which has an excellent machining property, a hard quality, a stable performance, a high cost performance and a wide applicability.
There are two types of rare earth magnets depending on the manufacturing method: one is sintered magnet and the other one is bonded magnet. The sintered magnet of which has wider applications. In the conventional technique, the process of sintering the rare earth magnet is mainly performed as follows: raw material preparing→melting→casting→hydrogen decrepitation (HD)→jet milling (JM)→compacting under a magnetic field→sintering→heat treatment→magnetic property evaluation→oxygen content evaluation of the sintered magnet→machining→surface treatment and so on.
The development history of the sintered rare earth magnet cannot be overly summarized in a word that it is the developing of improving the content rate of the main phase and reducing the constitute of the rare earth. Recently, to improve (BH)max and coercivity, the integral anti-oxidization technique of the manufacturing method is developing continuously, so the oxygen content of the sintered magnet can be reduced to below 2500 ppm at present; however, if the oxygen content of the sintered magnet is too low, the affects of some unstable factors like micro-constituent fluctuation or infiltration of impurity during the process may be amplified, so that it may result in over sintering, abnormal grain growth (AGG), low coercivity, low squareness, low heat resistance property and so on.